1. 備庫停止redo應用：
alter database recover managed standby database cancel;
2. 主庫重啟：
shutdown immediate;
startup mount
3. 主庫升級切換保護模式：
alter database set standby database to maximize availability;
（或者alter database set standby database to maximize protection;）
alter database open;
4. 備庫啟動redo應用：
alter database recover managed standby database disconnect from session;
降級切換步驟：
1. 備庫停止redo應用：
alter database recover managed standby database cancel;
2. 主庫調整保護模式：
alter database set standby database to maximize performance;
3. 備庫啟動redo應用：
alter database recover managed standby database disconnect from session;
